Time asymmetry in the palaeobiogeographic history of species

Abstract

The difficulties and hindrances of palaeobiogeography and historical biogeography in its long, sterile search for centres of origin or ancestral areas of species, leading some authors to withdraw the centre-of-origin as a non-scientific concept, are here considered as signals and not artefacts for the recognition of patterns in the biogeographic history of lineages. The time-symmetric model, which assumes gradual origination and extinction processes of a species, is here questioned and an alternative time-asymmetric model is proposed. The origination and expansion processes of a species history would be much faster and more unpredictable than the often gradual, long, predictable extinction process marked by previous signals of geographic area contraction. Monitored biological invasions, plankton blooms and episodes of coordinated migrations illustrate the fast expansion of novel species behaving as dissipative structures. The asymmetric biogeographic model is tested through palaeobiogeographic data on Old World mammal species and by the consistent preference of biostratigraphers for species appearance against species extinction as time-marker bioevents. Time-asymmetry is a common phenomenon of nature, indicating that asymmetry could well be a general property of Time itself. Asymétrie temporelle dans l'histoire paléogéobiographique des espècesMots-clés. -Paléobiogéographie, Espèces, Origine, Extinction, FAD, LAD, TempsRésumé. -Les difficultés et les obstacles de la paléobiogéographie et de la biogéographie historique rencontrés dans la longue et stérile recherche des centres d'origine ou d'« aires ancestrales » des espèces ont amené certains auteurs à abandonner ce concept non-scientifique. Les méthodes qualitatives et quantitatives utilisées pour repérer les aires d'origine des espèces sont confrontées à de sérieuses difficultés du fait des nombreuses hypothèses non vérifiées sur des probabilités ou des directions de dispersion. Aucun centre d'origine d'aucune espèce n'a jamais été documenté, sauf lorsqu'ils ont été rapportés à de très vastes régions (des continents ou des océans entiers). De nombreux auteurs ont renoncé à leur recherche. Ces difficultés sont ici considérées comme un signal, et non pas du bruit de fond, pour reconnaître des « patterns » cohérents dans l'histoire biogéographique des lignées.On assume couramment que dans l'histoire paléobiogéographique des espèces on doit trouver généralement des processus graduels d'apparition et d'extinction. Ce modèle symétrique dans le temps est ici remis en question et un modèle alternatif, asymétrique dans le temps, est proposé pour l'histoire des espèces. Selon notre modèle, les processus d'apparition et d'expansion des espèces seraient beaucoup plus rapides, courts et imprévisibles que les processus d'extinction, généralement lents, longs et prévisibles parce que précédés graduellement par des signes de diminution progressive par paliers de l'aire de distribution. Des monitorages d'espèces envahissantes, des floraisons instantanées en temps réel du plancto...

Documenting the biogeographic history ofMicrotus cabreraethrough its fossil record

“…During the Middle Pleistocene, Microtus brecciensis extended throughout the Iberian Peninsula, with the exception of the Cantabrian region and the North Atlantic facade (Ayarzagüeña & López Martínez , Cabrera‐Millet et al. , López‐Martínez ), and was found in the southern third of France (Marquet , Jeannet ) and in the Italian Peninsula, where records are common (Kotsakis et al. , Sala & Masini , Sala & Locatelli ).…”

“…We aim to reconstruct the biogeographic history of Microtus cabrerae from its fossil record in archaeological and palaeontological sites. Previous research has highlighted changes in the species' distribution over time but was based on few data (Ayarzagüeña & López Martínez 1976, Cabrera-Millet et al 1983, López-Martínez 2009, Garrido-García & Soriguer-Escofet 2012. We used every available record of the species found in the literature, throughout its whole geographic range and from its first appearance to the present, as well as a number of unpublished records from Spanish localities.…”

Agricultural intensification during the Late Holocene rather than climatic aridification drives the population dynamics and the current conservation status ofMicrotus cabrerae, an endangered Mediterranean rodent

“…The most accepted hypothesis explaining the current small fragmented distribution of M. cabrerae is that climatic conditions became less favourable (increase in aridity) during the Late Holocene. This hypothesis implies that human pressure only played a secondary role that is restricted to (sub)actual population declines (López‐Martínez, , ; Pita et al., ). Our results support the alternative hypothesis (Garrido‐García & Soriguer‐Escofet, ) that climate change during the Late Holocene would have led to an increase in the potential distribution (Figure , Table ).…”

“…Of the 19 bioclimatic variables, for both periods, we selected temperature seasonality (Tsea), minimum temperature of the coldest month (Tmin) and precipitation seasonality (Psea). To account for aridity (hypothesized as being responsible for the decline of M. cabrerae ; López‐Martínez, , ; Laplana & Sevilla, ), we calculated an aridity index (AI) using monthly precipitation and temperature values available in WorldClim, and defined as the fraction of the annual potential evapotranspiration (ETP) compensated by the annual precipitation (AI = ETP/AP) (details in Appendix S3).…”

“…Short‐term data highlighting the effects of human pressure (habitat losses through the expansion/intensification of croplands and animal husbandry) in combination with the species’ stenotopy as the principal threat factors (Pita et al., ). Conversely, long‐term data have been used to tentatively reconstruct its taxon history, with its emergence during the Marine Isotope State 5 (130–71 ka BP), expansion in the Early Holocene (10.5–7.5 ka BP), maximum/stasis in the Mid‐Holocene (7.5–5 ka BP) and a decline in the Late Holocene that led to its current situation (Garrido‐García & Soriguer‐Escofet, ; Laplana & Sevilla, ; López‐Martínez, , ). Three hypotheses have been proposed to explain the historical origin of this decline: (1) increased aridity at the beginning of the Subboreal period (5.3 ka BP; López‐Martínez, , ), (2) expansion and intensification of agriculture and animal husbandry during the Subatlantic period (2.5 ka BP; Garrido‐García & Soriguer‐Escofet, ) and (3) a combination of these two processes (Laplana & Sevilla, ).…”